The present invention relates to an optical deflector which reflects and deflects a light beam, and to a light scanning apparatus and a scanning type image display apparatus which use the same.
An optical deflector is a device changing a reflecting direction of a light beam from a light source. Scanning the light beam with the optical deflector can form an image. Light scanning apparatuses and scanning type image display apparatuses using such an optical deflector have been proposed in, for example, U.S. Pat. No. 5,467,104.
A micro mechanical system (Micro Electro-Mechanical System: MEMS) produced by semiconductor production processes is often used as the optical deflector (scanning device) as disclosed in Japanese Patent Laid-Open Nos. 7-175005 and 8-334723.
The optical deflector generally has a substrate portion and a reflecting surface (a mirror surface or a reflecting portion) supported thereby via torsion bars. The reflecting surface swing by an electromagnetic force or an electrostatic force provided from an actuator with the torsion bars being twisted. Such an optical deflector is extremely small and can operate fast.
In such an optical deflector, a larger reflecting surface than a diameter of the light beam entering the optical deflector can receive the entire light beam even when there is a positional error between the light beam and the reflecting surface. On the other hand, a large reflecting surface causes deterioration of mechanical characteristics of the optical deflector and increase of power consumption. It is therefore desirable that the reflecting surface be as small as possible.
As shown in FIG. 15, when a reflecting surface 1501 is smaller than the diameter of an incident luminous flux 1502, some of the light beam 1502 does not impinge on the reflecting surface 1501 and is reflected by a member disposed behind the reflecting surface 1501. Such unnecessary reflected light forms flare on a displayed image, which deteriorates quality of the image. Accordingly, it is desirable that the size of the reflecting surface be the same as the diameter of the light beam impinging thereon.
However, in a case where the size of the reflecting surface is the same as the diameter of the light beam, an incorrect (shifted) positional relationship between the light beam and the reflecting surface due to component tolerance and assembly error causes some of the light beam which does not impinge on the reflecting surface to reflect by the member disposed behind the reflecting surface, as is the case where the reflecting surface is smaller than the diameter of the light beam. Therefore, flare is generated.
On the other hand, in general, the diameter of the light beam entering the optical deflector is narrowed down by an aperture stop portion 1604 for beam shaping, the aperture stop portion 1604 being provided in a light source unit 1605 including a light source 1603. In order to cause the light beam 1606 shaped by the aperture of the aperture stop portion 1604 to impinge on the reflecting surface 1602 of the optical deflector 1601, high positional accuracy is required between the light source unit 1605 and the reflecting surface 1602.
In addition, when the distance from the light source 1603 to the optical deflector 1601 is long, diffraction may be caused by an aperture rim of the aperture stop portion 1604. That is, the diameter of the light beam 1606 reaching the optical deflector 1601 is larger than that of the light beam 1606 immediately after passing through the aperture stop portion 1604, which results in increase of the light beam that does not impinge on the reflecting surface 1602, and thereby the above-described unnecessary light component increases.